The move amounted to a major gamble by the Nevada Democrat, who is betting that he can sway the last few moderates onto his plan for a public option that would allow states to opt out by 2014.

But at the same time, Democratic Senate aides expressed worries that Reid was going too far, too fast with a strategy that allows no room for error.

And Reid’s move Monday seemed at odds with President Barack Obama, who has expressed a preference for pursuing a compromise that could win a filibuster-proof majority and some bipartisan support. But by all accounts, Reid has neither at this point.

The White House, however, issued a statement praising Reid’s move, saying that Obama is “pleased that the Senate has decided to include a public option for health coverage, in this case with an allowance for states to opt out. As he said to Congress and the nation in September, he supports the public option because it has the potential to play an essential role in holding insurance companies accountable through choice and competition.”

Reid’s announcement amounts to a dramatic bid to resuscitate the public option in the Senate after weeks of it appearing all but dead. Progressives — from the architect of the strategy, Sen. Chuck Schumer (D-N.Y.), to activist groups that pushed relentlessly for the public option — hailed Reid as bold and his move as a “huge victory.”

But the task ahead for Reid is steep, and at this point, even expert Senate vote-counters say there’s no way to know if Reid can pull it off. It all comes down to moderates — and Reid’s skill at convincing them the opt-out plan is not the budget-busting Big Government health takeover many worry about.

The early signs are not encouraging for Reid.

Two Democratic holdouts, Sens. Ben Nelson of Nebraska and Blanche Lincoln of Arkansas, have refused to commit to voting either way on the bill until they review it. And Sen. Olympia Snowe of Maine, the mostly likely Republican to support the bill, has said it would be “difficult” to support any bill with a government insurance option.

“I am deeply disappointed with the majority leader’s decision to include a public option as the focus of the legislation,” Snowe said in a statement Monday.

Reid is taking a calculated risk that he will be able to convince his 60-member caucus to stand by the bill, particularly when he needs them.

“As soon as we get the bill back from CBO and people have a chance to look at it, which we’ll have ample time to do that, I believe we clearly will have the support of my caucus to move to this bill and start legislating,” Reid said.

The notion was met with deep skepticism in the Senate, where each senator holds the power to torpedo a bill. Democratic aides speculated that Reid’s decision was motivated in part by electoral considerations. He faces a tough reelection next year, and this move is bound to shore up his left flank, which has derided him over the years as cautious and too willing to compromise.

Reid could get 60 votes to begin debate on the bill, largely because Democrats will not want to be seen as blocking health care reform at the outset, especially now that their leader has made such a public push to achieve it.

However, the challenge is securing 60 votes to move to final passage of the bill. It is difficult for Reid to game out the vote count that far because of the unpredictability of the floor debate. But it is precisely what’s giving some Democrats pause.

“If we can’t produce 60, you’ve got two choices: Pull the bill, or amend it. And amending it means that you’ll also need 60,” said a Senate Democratic aide. “The question is if the handful of moderates stay resolute and oppose cloture on the bill, then we’ll have to convince liberals to vote to weaken the public option. And that may be a very tough hill to climb because some of them may say they’d just as soon go to reconciliation than to compromise at that point.”

The majority leader’s staff told Democratic officials Monday that they hoped Reid’s decision would quell the public option debate within the next day or so and they could move on to other issues. Also, they said it “gets the left to leave them alone for awhile,” according to one official.

Indeed, the left was jubilant Monday.

“We haven’t won yet, not by a long shot, but we’ve passed a big milestone — we have a bill going to the Senate floor with a public health insurance option, something the pundits in Washington predicted would never happen,” an organizer for Health Care for America Now, a liberal group, wrote in an e-mail to supporters.

Under Reid’s proposal, nonprofit insurance cooperatives, which were included the Senate Finance bill, would also be offered in a new insurance marketplace known as an exchange. But if a state chose to opt out of the public option, they could not offer a co-op to replace it, according to Reid’s office.

Reid sent several concepts Monday to the Congressional Budget Office for a cost analysis. He forwarded only one version of the public option, but he included several variations of an insurance tax and options to make coverage more affordable, aides said.

Reid is looking to bump up the threshold at which insurers would pay a tax on high-end plans — from $21,000, for a family plan under the Finance bill, to $23,000, according to a person familiar with the negotiations.

Reid’s decision on the public option comes at a time when many in the midst of the Senate negotiations are expressing frustration that the White House hasn’t articulated a clear preference for what form a public option should take — or even if the public plan is a pre-condition of any deal.

Obama left the impression in a meeting Thursday that he was leaning toward the “trigger” idea floated by Snowe, a Democratic source said. Senate Majority Whip Dick Durbin (D-Ill.) said that the White House and Democratic leaders want Snowe’s support but determined that to do that — by adding a provision that would “trigger” a public plan if private insurers don’t control costs — would lose too many Democrats.